Alloy production by vapor condensation

Abstract

In the production of alloy by evaporation from an evaporation bath and condensation under vacuum, charge replenishment is achieved by a procedure involving bleeding charge from the bath and admixing the bled charge with replenishment material and introducing replenishment from the admixture. An apparatus for use in the process comprises a mixing passageway encompassing an evaporation bath and distributed sub-surface bleed ports and feed ports linking the evaporation bath and the mixing chamber. Flow of metal through the ports is induced by pumped circulation in the mixing chamber. The circulation is turbulent for good mixing of the metals.

We claim: 
     
       1. A method for the replenishment of charge material within an evaporation bath, in a process for the production of alloy by evaporation of molten alloy from the evaporation bath and condensation of the vapor upon a temperature controlled collector all under vacuum conditions wherein said method comprises the following preliminary steps: providing a charge of molten degassed metal in an evaporation bath;   melting and outgassing feedstock metal in a feedstock melting chamber;   passing molten metal from the evaporation bath and from the feedstock melting chamber to a mixing chamber;   and comprises the following steps which are maintained through the production process:   pumping the molten metal in the mixing chamber to cause turbulent flow therein and thereby cause mixing of the source metals therein;   bleeding a portion of the evaporation bath charge and introducing the bled charge metal into the mixing chamber through a plurality of spaced apart sub-surface bleed passageways which link the evaporation bath with the mixing chamber;   feeding a portion of the mixed metals from the mixing chamber into the evaporation bath through a plurality of spaced apart sub-surface feed passageways which link the mixing chamber with the evaporation bath; and   maintaining metal in the mixing chamber by replenishment with molten metal from the feedstock melting chamber.   
     
     
       2. A method as claimed in claim 1 wherein the bleeding is caused by the circulation within the mixing chamber. 
     
     
       3. A method as claimed in claim 2 wherein the feeding is caused by the circulation within the mixing chamber. 
     
     
       4. A method as claimed in claim 1 wherein a bleed rate is established which is 10-20 times the rate of evaporation from the evaporation bath. 
     
     
       5. A method as claimed in claim 3 wherein a bleed rate is established which is 10-20 times the rate of evaporation from the evaporation bath. 
     
     
       6. A method as claimed in claim 4 wherein a flow rate is established in the mixing chamber which is at least 70 times the evaporation rate. 
     
     
       7. A method as claimed in claim 5 wherein a flow rate is established in the mixing chamber which is at least 70 times the evaporation rate. 
     
     
       8. An apparatus for the replenishment of charge material within an evaporation bath wherein the apparatus comprises: i. an evaporation bath;   ii. a mixing chamber consisting of a passageway encompassing the evaporation bath;   iii passageways linking the interior of the evaporation bath to the mixing chamber the passageways forming two groups each group comprising a plurality of such passageways issuing from the evaporation bath at spaced-apart sub-surface locations therein;   iv. pump means operable to cause turbulent flow of liquid metal along the mixing chamber passageway;   v. bleed means operable to cause withdrawal of liquid metal from the evaporation bath through the passageways of one of the aforementioned groups; and   vi. feed means operable to cause introduction of liquid metal to the evaporation bath through the passageways of the remaining group.   
     
     
       9. An apparatus as claimed in claim 8 wherein the bleed means comprises a divergent section of the mixing chamber passageway such that the withdrawal of liquid metal from the evaporation bath is produced by a decrease in hydrodynamic pressure in the mixing chamber contents consequent upon the flow through the divergent section. 
     
     
       10. An apparatus as claimed in claim 9 wherein the feed means comprises a convergent section of the mixing chamber passageway such that the introduction of liquid metal into the evaporation bath is produced by an increase in the hydrodynamic pressure in the mixing chamber contents consequent upon the flow through the convergent section. 
     
     
       11. An apparatus as claimed in claim 10 wherein the pump means comprises an electromagnetic pump. 
     
     
       12. An apparatus as claimed in claim 10 comprising a feed stock melting chamber, means to melt metal therein, and a sub-surface passageway linking the melting chamber to the mixing chamber. 
     
     
       13. An apparatus as claimed in claim 10 wherein the divergent section has an increase in cross section in the range 7-30%. 
     
     
       14. An apparatus as claimed in claim 13 wherein the convergent section has a decrease in cross section in the range 7-30%.